Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-à-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
The heparin-binding growth factors (HBGFs) constitute a large class of growth factors that includes the 23 fibroblast growth factors identified to date (FGFs 1-23), HBBM (heparin-binding brain mitogen), HB-GAF (heparin-binding growth associated factor), HB-EGF (heparin-binding EGF-like factor) HB-GAM (heparin-binding growth associated molecule), TGF-α (transforming growth factor-α), TGF-βs (transforming growth factor-(βs), PDGF (platelet-derived growth factor), EGF (epidermal growth factor), VEGF (vascular endothelial growth factor), IGF-1 (insulin-like growth factor-1), IGF-2 (insulin-like growth factor-2), HGF (hepatocyte growth factor), IL-1 (interleukin-1), IL-2 (interleukin-2), IFN-α (interferon-α), IFN-γ (interferon-γ), TNF-α (tumor necrosis factor-α), SDGF (Schwannoma-derived growth factor) and the many other growth factors, cytokines, lymphokines and chemokines that have an affinity for heparin.
Peptides from natural HBGFs that bind heparin-binding growth factor receptors have been identified. See for example Ray et al., Proc. Natl. Acad. Sci. USA 94:7047-7052 (1997). These authors demonstrated that two amino acid sequences from FGF-2 are sufficient to block the mitogenic activity of FGF-2 on neural progenitor cells. The first peptide is a ten amino acid sequence, from amino acids 65-74, the second peptide extends from amino acids 115-129.
In an alternative approach, an artificial peptide that binds a heparin-binding growth factor receptor was identified by a phage display method. Ballinger et al., Nature BioTechnology 17:1199-1204 (1999) used this technique to isolate a 28 amino acid peptide called C19, binds FGF-2 receptors, but by itself fails to stimulate biological activity. The peptide has no amino acid sequence identity with any known FGF.
HBGFs useful in prevention or therapy of a wide range of diseases and disorders may be purified from natural sources or produced by recombinant DNA methods, however, such preparations are expensive and generally difficult to prepare.
Some efforts have been made to generate heparin-binding growth factor analogs. For example, natural PDGF occurs as an A chain and a B chain arranged in head-to-head (AA or BB) homodimers, or (AB or BA) heterodimers. Thus, U.S. Pat. No. 6,350,731 to Jehanli et al. discloses PDGF analogs in which two synthetic PDGF receptor-binding domains are covalently linked through a polyglycine or an N-(4-carboxy-cyclohexylmethyl)-maleimide (SMCC) chain to mimic the natural active polypeptide dimer.
U.S. Pat. No. 6,235,716 to Ben-Sasson discloses analogs of angiogenic factors. The analogs are branched multivalent ligands that include two or more angiogenic homology regions connected by a multilinker backbone.
U.S. Pat. No. 5,770,704 (the '704 patent) to Godowski discloses conjugates for activating receptor tyrosine kinases, cytokine receptors and members of the nerve growth factor receptor superfamily. The conjugates include at least two ligands capable of binding to the cognate receptor, so that the binding of the respective ligands induces oligomerization of these receptors. The ligands disclosed in the '704 patent are linked by covalent attachment to various nonproteinaceous polymers, particularly hydrophilic polymers, such as polyvinylalcohol and polyvinylpyrrolidone, and the polyvinylalkene ethers, including polyethylene glycol and polypropylene glycol. The ligands include hepatocyte growth factor (HGF) peptide variants that each bind HGF receptor, thereby causing receptor dimerization and activation of the biological activity of the HGF receptor dimer.
U.S. Pat. No. 6,284,503 (the '503 patent) to Caldwell et al. discloses a composition and method for regulating the adhesion of cells and biomolecules to hydrophobic surfaces and hydrophobic coated surfaces for cell adhesion, cell growth, cell sorting and biological assays. The composition is a biomolecule conjugated to a reactive end group activated polymer. The end group activated polymer includes a block copolymer surfactant backbone and an activation or reactive group. The block copolymer may be any surfactant having a hydrophobic region capable of adsorbing onto a hydrophobic surface, and a hydrophilic region which extends away from the surface when the hydrophobic region is adsorbed onto the hydrophobic surface. The '503 patent discloses that the biomolecules that may be conjugated to the end group activated polymer include natural or recombinant growth factors, such as PDGF, EGF, TGFα, TGFβ, NGF, IGF-I, IGF-II, GH and GHRF, as well as multi-CSF(II-3), GM-CSF, G-CSF, and M-CSF.
Other workers have described compositions that include homologs and analogs of fibroblast growth factors (FGFs). See for example U.S. Pat. No. 5,679,673 to Lappi and Baird; U.S. Pat. No. 5,989,866 to Deisher et al. and U.S. Pat. No. 6,294,359 to Fiddes et al. These disclosures relate to FGF homologs or analogs that are either conjugated to a toxic moiety and are targeted to the FGF receptor-bearing cells; or are homologs or analogs that modulate the biological pathways through the signal transduced by the FGF receptor upon binding by the FGF homolog or analog.
A series of patent applications to Kochendoerfer et al. disclose polymer-modified proteins, including synthetic chemokines and erythropoiesis stimulating proteins. See, for example, International Publications WO 02/04105, WO 02/19963 and WO 02/20033. These include chemically ligated peptide segments of a polypeptide chain of a synthetic erythropoiesis protein, such that a polypeptide chain results, with a water soluble polymer attached at one or more glycosylation sites on the protein. These applications also disclose synthetic chemokines, which are also polymer modified, and are asserted to be antagonists. However, heparin-binding domains are not disclosed. Other erythropoietin mimetics are known, such as those disclosed in U.S. Pat. Nos. 5,773,569 and 5,830,851 to Wrighton et al.
International Publication WO 00/18921 to Ballinger and Kavanaugh discloses a composition consisting of fusion proteins having FGF receptor affinity linked to an “oligomerization domain”, either directly or through a linking group. The oligomerization domain ranges in length from about 20 to 300 residues, and includes constructs such as transcription factors, Fc portions of IgG, leucine zippers and the like. The oligomerization domains disclosed are homodimeric domains, wherein a single FGF receptor affinity fusion protein is linked to a single domain, such as a leucine zipper, which in turn is linked to a similar molecule by means of cysteine residues at both the amino and carboxy termini of the leucine zippers, such that two parallel leucine zippers, each with a single FGF receptor affinity fusion protein, are cross-linked by means of disulfide bonds. It is also disclosed that fusion proteins may include a heparin-binding domain, such as the use of jun as a multimerization domain, which is asserted to be a heparin binding domain. Thus the compositions disclosed by Ballinger and Kavanaugh are all composed of a single receptor-binding sequence covalently attached to an oligomerization domain, whereby two or more similar oligomerization domains, each with a single receptor-binding sequence, are conjoined by means of either an association provided by the oligomerization domain, or alternatively, are chemically cross-linked to provide for the covalent bonding of the individual components.
The above described homologs, analogs, conjugates or ligands each include a receptor-binding domain. However, none of the disclosed compositions further include both a linker, providing for the linking of two receptor-binding domains to a dipeptide sequence, and further providing a single non-signaling peptide containing a heparin-binding domain. Moreover, none of these or other known heparin-binding growth factor analogs provide the advantages described herein below. There is still a need for new peptide analogs of HBGFs, particularly for those that function as agonists. In particular, there is still a need for cost-effective synthetic peptide agonists of heparin-binding growth factor receptors, particularly synthetic heparin-binding growth factor agonists useful for coating medical devices and as soluble biologics.